1. Field of the Art
The present invention relates to Ziegler polymerization of olefins. More particularly, the present invention is concerned with Ziegler polymerization of olefin, or .alpha.-olefins of at least 3 carbon atoms, in particular, characterized by, among others, the solid catalyst components comprising a transition metal in Ziegler catalysts.
Use of the solid catalyst component in accordance with the present invention in Ziegler catalysts as the transition metal component will make it possible to produce polymers endowed with improved stereoregularity in an improved yield with decreased production of by-product polymers.
2. Background of the invention
The catalysts heretofore proposed for the polymerization of olefins comprising a solid catalyst component containing titanium, magnesium and a halogen as the essential ingredients and an organoaluminum have very high activity, but require the use of an electron donor compound during polymerization as what is called "outside electron donor" when the sterecspecificity of the product polymers is to be improved.
However, the catalysts in which an electron donor is used entail such problems that the electron donor used may react with the organoaluminum compound used thereby lowering the polymerization velocity and the reaction of the electron donor with the organoaluminum compound is accelerated upon increase in the temperature whereby higher polymerization should be avoided, which will in turn result in several disadvantages such that it will be restricted to increase productivity inherent in increasing the polymerization temperature or it will be difficult to control performance of the product polymers such as to control molecular weight of the polymers. Furthermore, it may require a considerable amount of an electron donor in order to obtain the stereospecificity of the polymers at a desired level, whereby the product polymers which may be obtained without undergoing the catalyst removal step may have odor of the electron donor used.
Accordingly, it has teen desired to develop catalysts which produce highly stereospecific polymers in a high yield without use of an electron donor as the outside electron donor.
Japanese Patent Laid-Open Publication No. 138715/1983 discloses catalysts for polymerization which do not require the outside electron donor, which catalysts comprise an organoaluminum compound and a solid component which has been prepared by contacting a titanium complex (1) comprising a tetra-valent titanium, magnesium, a halogen and an electron donor with an organosilicon compound (2) having a bond of Si--O--C in the presence of an organoaluminum compound or after the titanium complex (1) having been treated with an organoaluminum compound.
This proposal may have succeeded in solving the problems referred to, but may still entail problems such that the polymer performance may not be improved to a desired level and the proportions of the titanium component to the organoaluminum component may be confined in a certain range.
Japanese Patent Laid-Open Publication No. 187707/1987 proposes the use of a certain specified organoalkoxysilicon compound, which appears to have removed, in considerable degree, the necessity that an organoaluminum compound used in the polymerization be in a confined range. However, the activity of the catalyst in view of the polymer yield obtained is not shown therein to be always at a level where no catalyst removal processing is required especially when the molecular weight control or production of copolymers is desired, whereby further improvement may be desired.
On the other hand, Japanese Patent Laid-Open Publication Nos. 15804/1988, 68622/1988, 68648/1988, 69809/1988, 278502/1989, 279940/1989 and 282203/1989 disclose catalysts which have been treated by a trialkylarylsilane or by a trialkylvinylsilane or catalysts which have a polymer of a trialkylarylsilane or a trialkylvinylsilane contained therein will work as nucleating agent in the polymers thereby produced whereby the polymers produced are improved in transparency and stiffness.
The proposals may be appreciated since the crystallinity of the polymers may have been increased due to the reduction in size of the spherulites, but the problems that by-product polymers are formed and the catalyst activity is not very high still remain unsolved.